In earlier Dukoral cholera vaccine studies in Bangladesh, 56% of the recipient children aged 6 months to 2 years responded with vibriocidal antibodies ; For the Vivotif vaccine data from vaccines aged >6 years documented 67% seroconversion. The sample sizes for different components of the study have been calculated based on the assumption that 50% of children will respond to Vivotif. Based on the results obtained with zinc supplementation on the immune response to Dukoral, that observed increase in the rates with supplementation from 56% to 79% , and assuming a 30% increase in responses to Vivotif (with around 15 attrition rates) the sample size will be 75 in each group (with and without zinc).